Liquid crystal display units and touch panels (touch sensors) are used in display devices including large electronic devices such as personal computers and televisions and miniature electronic devices such as car navigation systems, cellular phones and electronic dictionaries or OA⋅FA devices. Such liquid crystal display units and touch panels are provided with electrodes composed of transparent conductive electrode materials. As transparent conductive electrode materials there are known ITO (Indium-Tin-Oxide), indium oxide and tin oxide, which materials exhibit high visible light transmittance and are therefore the major materials used as electrode materials for liquid crystal display unit boards.
Various types of systems are already being implemented for touch panels, but in recent years the use of electrostatic capacitive touch panels has been progressing. In an electrostatic capacitive touch panel, contact of the fingertip (a conductor) with the touch input screen causes electrostatic capacitive coupling between the fingertip and the conductive film, forming a condenser. Thus, an electrostatic capacitive touch panel detects changes in electrical charge at sites of contact with the fingertip, thereby determining the coordinates.
In particular, projection-type electrostatic capacitive touch panels have satisfactory operativity allowing complex instructions to be carried out since they allow multipoint fingertip detections, and the excellent operativity has led to their utilization as input devices on the display surfaces of devices with small displays such as cellular phones, portable music players and the like.
For representation of two-dimensional coordinates with an X-axis and a Y-axis, a projection-type electrostatic capacitive touch panel generally has a plurality of X-electrodes and a plurality of Y-electrodes perpendicular to the X-electrode forming a two-layer structure, with ITO (Indium-Tin-Oxide) employed as the electrodes.
Incidentally, since the frame region of a touch panel is a region where detection of the touch location is not possible, reducing the area of the frame region has been an important goal in order to increase product value. The frame region requires metal wiring in order to transmit the detection signal of a touch location, but the width of the metal wiring must be narrowed to reduce the frame area. Because of the insufficiently high conductivity of ITO, metal wirings are generally formed of copper.
However, in the touch panels mentioned above, corrosive components such as moisture and salts can infiltrate from the sensing region into the interior upon contact with the fingertip. When corrosive components infiltrate into the interior of a touch panel, the metal wiring may corrode, electrical resistance between the electrodes and driving circuits may increase, and wire breakage can occur.
In order to prevent corrosion of metal wirings, there have been disclosed electrostatic capacitive projection-type touch panels with insulating layers formed on metals (Patent document 1, for example). In such touch panels, a silicon dioxide layer is formed on metal by a plasma chemical vapor deposition method (plasma CVD), thereby preventing corrosion of the metal. However, because such methods employ plasma CVD, they require high-temperature treatment, and therefore the base materials are limited and production cost is increased.
Incidentally, known methods for providing resist films on necessary locations include methods in which a photosensitive layer comprising a photosensitive resin composition is provided on a prescribed base material and the photosensitive layer is exposed and developed (Patent documents 2 to 4, for example). Also, Patent documents 5 and 6 disclose formation of protective coats for touch panels by such methods.